Inner ear disorders of hearing and balance affect over 30 million Americans, many of whom are children. The goal of this research is to elucidate the cellular and molecular processes that underlie sensory organogenesis during inner ear development. The proposed research will use the acoustico-vestibular systems of Xenopus laevis and Xenopus (Silurana) tropicalis to obtain comparative data about the structure, physiology, and genetic profile of three inner ear endorgans: the sacculus (an acoustico-vestibular organ), the utricle (a vestibular organ) and the amphibian papilla (an acoustic organ). Experiments will focus on mechanosensory hair cells and sensory ganglion cells with the aim of determining how these ceils of the peripheral nervous system acquire their unique phenotype during development. Experiments also aim to discern how mechanosensory hair cells can be restored or regenerated to their normal phenotype after damage or trauma. The specific aims are: (1) to obtain structural and physiological data about the comparative development of the utricle, amphibian papilla, and sacculus, (2) to initiate studies of mechanosensory hair cell development and regeneration using an in vitro culture system, and (3) to determine the function and developmental expression patterns of genes screened from inner ear cDNA libraries. Anatomical and molecular data gathered as part of this research will be prepared for dissemination in the public domain via online databases. Methods used in this research include cell culture, immunohistochemistry, patch clamp, multiphoton and confocal microscopy, RT-PCR directed cDNA library construction, and yeast two hybrid analysis. A technical objective of this research is to develop methods for vital imaging of ceils and organs of the inner ear. Experimental results will provide fundamental data about hair cell differentiation and proliferation during sensory organogenesis, and will increase knowledge of the genetics of the acoustico-vestibular systems. A long term goal of this research is to determine how genes expressed in the inner ear are regulated during development, regeneration, and aging. These investigations aim to produce results with applicability for the development of treatments for hereditary and environmentally-induced disorders of heanng and balance.